Change of Lanes

I was once told by mom that it doesn't matter how many times you change lane, the lane the you just changed from will go faster than the lane you are right now. Why is that so true? I was running a little bit late today, and so was the lane in which I was, so as any normal person would, I changed lanes. The lane that I changed to completely stopped, and then when I thought it was finally moving again, the guy in front of me decides to make a turn and completely stops while making a turn. That lane change added about 10 extra minutes to my trip. So be very careful when you change lanes!